The present invention relates to backing members for holding microelectronic-device substrate assemblies to a carrier head in mechanical and/or chemical-mechanical planarization processes. More particularly, the present invention relates to backing members that hold a substrate assembly to a carrier head via a vacuum force during planarization of the substrate assembly on a polishing pad.
Mechanical and chemical-mechanical planarizing processes (collectively xe2x80x9cCMPxe2x80x9d) are used in the manufacturing of microelectronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic-device substrate assemblies. CMP processes generally remove material from a substrate assembly to create a highly planar surface at a precise elevation in the layers of material on the substrate assembly.
FIG. 1 schematically illustrates an existing web-format planarizing machine 10 for planarizing a substrate assembly 12. The planarizing machine 10 has a support table 14 with a top panel 16 at a workstation where an operative portion (A) of a polishing pad 40 is positioned. The top panel 16 is generally a rigid plate to provide a flat, solid surface to support the operative section of the polishing pad 40 during planarization.
The planarizing machine 10 also has a plurality of rollers to guide, position and hold the polishing pad 40 over the top panel 16. The rollers include a supply roller 20, first and second idler rollers 21a and 21b, first and second guide rollers 22a and 22b, and a take-up roller 23. The supply roller 20 carries an unused or preoperative portion of the polishing pad 40, and the take-up roller 23 carries a used or post-operative portion of the polishing pad 40. Additionally, the first idler roller 21a and the first guide roller 22a stretch the polishing pad 40 over the top panel 16 to hold the polishing pad 40 stationary during operation. A drive motor (not shown) drives at least one of the supply roller 20 and the take-up roller 23 to sequentially advance the polishing pad 40 across the top panel 16. As such, clean preoperative sections of the polishing pad 40 may be quickly substituted for used sections to provide a consistent surface for planarizing the substrate assembly 12.
The web-format planarizing machine 10 also has a carrier assembly 30 that controls and protects the substrate assembly 12 during planarization. The carrier assembly 30 generally has a carrier head 31 with a plurality of vacuum holes 32 to pick up and release the substrate assembly 12 at appropriate stages of the planarizing cycle. A plurality of nozzles 41 attached to the carrier head 31 dispense a planarizing solution 42 onto a planarizing surface 43 of the polishing pad 40. The carrier assembly 30 also generally has a support gantry 34 carrying a drive assembly 35 that translates along the gantry 34. The drive assembly 35 generally has actuator 36, a drive shaft 37 coupled to the actuator 36, and an arm 38 projecting from the drive shaft 37. The arm 38 carries the carrier head 31 via another shaft 39 such that the drive assembly 35 orbits the carrier head 31 about an axis Bxe2x80x94B offset from a center point Cxe2x80x94C of the substrate assembly 12.
Many planarizing machines also use a substrate backing member 50 in the carrier head 31 to support a backside of the substrate assembly 12. The backing member 50 is typically a perforated, flexible pad positioned between the carrier head 31 and the substrate assembly 12. The perforations through the backing member 50 are generally a plurality of uniform pores or holes (not shown) that directly transfer a vacuum force from each vacuum hole 32 in the carrier head 31 to a backside 15 of the substrate assembly 12. In operation, the vacuum force is drawn against the backside 15 of the substrate assembly 12 through the perforated backing member 50 to pick up the substrate assembly 12 from a load station (not shown) or the polishing pad 40.
The polishing pad 40 and the planarizing solution 42 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate assembly 12. The web-format planarizing machine 10 typically uses a fixed-abrasive polishing pad having a plurality of abrasive particles fixedly bonded to a suspension material. The planarizing solutions used with fixed-abrasive pads are generally xe2x80x9cclean solutionsxe2x80x9d without abrasive particles because additional abrasive particles in conventional abrasive CMP slurries may ruin the abrasive surface of fixed abrasive pads. In other applications, the polishing pad 40 may be a nonabrasive pad composed of a polymeric material (e.g., polyurethane), a resin, or other suitable materials without abrasive particles. The planarizing solutions 42 used with nonabrasive polishing pads are typically xe2x80x9cabrasivexe2x80x9d CMP slurries with abrasive particles.
To planarize the substrate assembly 12 with the planarizing machine 10, the carrier assembly 30 presses the substrate assembly 12 against the planarizing surface 43 of the polishing pad 40 in the presence of the planarizing solution 42. The drive assembly 35 then orbits the carrier head 31 about the offset axis Bxe2x80x94B to translate the substrate assembly 12 across the planarizing surface 43. As a result, the abrasive particles and/or the chemicals in the planarizing medium remove material from the surface of the substrate assembly 12.
CMP processes should consistently and accurately produce a uniformly planar surface on the substrate assembly 12 to enable precise fabrication of circuits and photo-patterns. For example, during the fabrication of transistors, contacts, interconnects and other components, many substrate assemblies develop large xe2x80x9cstep heightsxe2x80x9d that create a highly topographic surface across the substrate assembly 12. To enable the fabrication of integrated circuits with high densities of components, it is necessary to produce a highly planar substrate surface at several stages of processing the substrate assembly 12 because non-planar substrate surfaces significantly increase the difficulty of forming submicron features. For example, it is difficult to accurately focus photo-patterns to within tolerances of 0.1 xcexcm on nonplanar substrate surfaces because submicron photolithographic equipment generally has a very limited depth of focus. Thus, CMP processes are often used to transform a topographical substrate surface into a highly uniform, planar substrate surface.
In the competitive semiconductor industry, it is also highly desirable to have a high yield of operable devices after CMP processing by quickly producing a uniformly planar surface at a desired endpoint on a substrate assembly. For example, when a conductive layer on the substrate assembly 12 is under-planarized in the formation of contacts or interconnects, many of these components may not be electrically isolated from one another because undesirable portions of the conductive layer may remain on the substrate assembly 12. Additionally, when a substrate assembly 12 is over-planarized, components below the desired endpoint may be damaged or completely destroyed. Thus, to provide a high yield of operable microelectronic devices, CMP processing should quickly remove material until the desired endpoint is reached.
One manufacturing concern of CMP processing is slippage between the substrate assembly 12 and the carrier head 31 during planarization. Such slippage is problematic because displacement between the substrate assembly 12 and the carrier head 31 during planarization may crack the substrate assembly 12, damage individual devices, or produce inconsistent planarizing results that cause localized under-planarization or over-planarization on the substrate assembly 12.
Existing techniques to inhibit or prevent slippage between the substrate assembly 12 and the carrier head 31 include coating the backside of the substrate assembly 12 with a wax or fluid, or drawing a vacuum through the carrier head 31 against the substrate assembly 12. Yet, as the continual drive to miniaturize components requires planar surfaces to be within xc2x1100 xc3x85 of a desired endpoint, these existing techniques for holding the substrate assembly 12 to the carrier head 31 generally limit the ability to produce an adequately planar surface on the substrate assembly 12. Waxes and fluids are not suitable because they can distort the shape of the substrate assembly 12 and/or contaminate the materials on the substrate assembly 12. Moreover, drawing a vacuum against the backside 15 of the substrate assembly 12 during the planarizing cycle is not suitable because the vacuum force deforms the substrate assembly 12 at areas proximate to the vacuum ports 32 in the carrier head 31. Although such local deformations of the substrate assembly 12 may be slight, they generally create variations on the planarized substrate surface greater than xc2x1100 xc3x85. Therefore, many highly demanding CMP applications do not apply waxes, fluids or a vacuum force to the backside of a substrate assembly during a planarizing cycle.
In light of the problems associated with holding a substrate assembly to a carrier head during a planarizing cycle, many planarizing machines rely on a retaining ring depending from the carrier head 31 to retain the substrate assembly. Referring to FIG. 1, for example, a retaining ring 33 depends from the carrier head 31 to form a cavity in which the backing member 50 and the substrate assembly 12 are positioned. The retaining ring 33, however, typically engages the abrasive particles on the planarizing surface 43 of the polishing pad 40 during the planarizing cycle. As such, retaining rings are replaced periodically, which increases the costs for maintaining and repairing planarizing machines. The substrate assembly 12, moreover, may still slip out underneath the retaining ring during the planarizing cycle. Therefore, retaining rings do not resolve some of the drawbacks of holding a substrate assembly under a carrier head during planarization.
The present invention is directed toward devices and methods for releasably attaching substrate assemblies to carrier heads of planarizing machines in mechanical and/or chemical-mechanical planarization of microelectronic-device substrate assemblies. One aspect of the invention is a backing member for use in a carrier head to selectively couple a substrate assembly to the carrier head via a vacuum force before, during and after planarizing the substrate assembly.
The backing member can include a body having a first section with a first surface configured to be received by the carrier head and a second section with a second surface configured to support a backside of the substrate assembly. The first and second sections of the body are preferably composed of flexible, incompressible materials. The backing member also includes a first vacuum passageway extending through the body and a plurality of second vacuum passageways coupled to the first passageway and the second surface of the body. The first passageway is configured to be coupled to a vacuum source, and each second passageways extend from the first passageway to corresponding openings at the second surface of the body. The second passageways are preferably configured to distribute the vacuum force across the backside of the substrate assembly in a manner that prevents or at least substantially inhibits deformation of the substrate assembly so that the vacuum force does not adversely affect the planarity of the finished substrate surface.
In further aspects of the invention, the first passageway defines a primary conduit, such as a channel or a grid of channels, extending along a lower surface of the first section. The second passageways define secondary conduits, such as small holes or pores, extending through the second section of the backing member. The secondary conduits preferably extend from the primary conduit to a contact surface defined by the second surface of the body. In operation, the primary conduit in the first section distributes the vacuum force in a first distribution, and the secondary conduits redistribute the vacuum force in a second vacuum distribution at the contact surface for coupling the substrate assembly to the carrier head.